Depilation with a chlorite and hydrogen peroxide or a perborate



United States Patent 3,445,178 DEPILATlON WITH A CHLORITE AND HYDRO- GEN PEROXIDE OR A PERBORATE Fritz Hahn, Frankfurt am Main, Germany, assignor to Deutsche Goldund Silber-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany No Drawing. Filed Apr. 7, 1966, Ser. No. 540,856 Claims priority, application Germany, Apr. 8, 1965, D 46,987 Int. Cl. C14c 1/06 US. Cl. 8-94.16 6 Claims ABSTRACT OF THE DISCLOSURE Skins and hides are unhaired by contacting such skins and hides with an acidified aqueous chlorite solution containing an effective amount of an inorganic per compound selected from the group consisting of hydrogen peroxide and adducts of hydrogen peroxide to prevent substantial liberation of C10 and C1 during the unhairing treatment.

The invention relates to a process for unhairing skins and hides with the aid of chlorites in an acid aqueous medium which renders it possible to hinder the evolution of C10 and C1 and to shorten the time required for the unhairing treatment while preserving the skins and hides which are to be processed to leather.

In recent times an unhairing process using sodium chlorite has become known in which C10 has been designated as the agent responsible for the dissolution of the hair. Investigations, however, have shown that in dilute aqueous solutions of sodium chlorite which have been acidified with organic acids it is the chlorous acid (HClO and not the C10 which is responsible for the attack on the keratin of the hair. In the process described the alkaline sodium chlorite solution is aciditied with glycolic acid to provide a pH of 3.5. The quantities of C10 produced thereby cause a considerable odor problem. In addition, in the oxidation of keratin with HClO or C10 gaseous chlorine is formed which also is a respiratory poison. In addition, the chlorine formed, as a strong oxidizing agent, has a destructive eliect upon the native collagen fibers which becomes evident in a reduced tearing strength of leather produced from the treated skins.

The object of the invention is to provide a process for unhairing skins and hides with chlorites in an aqueous acid medium which avoids or at least reduces to a minimum the disadvantages described above of the production of C10 and C1 and the attack on the collagen engendered thereby.

The essence of the invention resides in the addition of an inorganic per compound, such as, hydrogen peroxide, or compounds containing such compound as an adduct, such as, alkali metal perborates, to the chlorite solution. Expediently, for example, at least over 25% by weight of an alkali metal perborate, such as sodium perborate, with reference to chlorite are employed and preferably 5- 8 parts by weight of such perborate are employed per 7-8 parts parts by weight of chlorite, such as, sodium chlorite. Equivalent proportions of other per compounds can be used. With the unhairing solutions employed according to the invention the C10 produced by the reaction is again reduced to HClO and therefore again made available for the oxidation of keratin. At the same time the chlorine also is reduced so that an attack on the collagen is hindered. As a result a better quality of leather can be produced from skins and hides which have been unhaired according to the invention. As the evolution of tangible quantities of C10 and C1 is prevented, odor 3,445,178 Patented May 20, 1969 problems as well as dangers to the health of the operator are avoided.

The weak and rather expensive glycolic acid which was previously used to acidity the chlorite solutions, was used for the purpose of reducing the development of C10 but such acid is not in a position to avoid production of C10 In contrast thereto the present process permits use of cheap acids, both organic and inorganic, such as, formic acid, acetic acid, sulfuric acid or phosphoric acid, as the development of C10 is hindered or reduced to a minimum by the addition of the perborate or other equivalent per compound.

Preferably the pH of the acid chlorite and per compound containing unhairing solutions employed according to the invention are adjusted to a pH of about 3.0 to 3.8.

The acidified chlorite solutions employed according to the invention preferably contain about 30 g. to g. per liter of sodium chlorite or equivalent quantities of other chlorites.

It was found that the use of neutral salts or weakly alkaline salts sometime after the unhairing treatment has begun will cause a more rapid dissolution of the tough oxidation products of the hair which are formed and therefore renders such oxidation products more easy to remove. Illustrative examples of suitable neutral or weakly alkaline salts are ammonium sulfate, disodium hydrogen phosphate, ammonium carbonate, sodium bicarbonate, sodium carbonate, borax, potassium carbonate, trisodium phosphate, or eventually ammonia as base. These salts shall have a bufiering effect and resulting in a solution with a pH value of 7.0 or above. Besides, these salts must be easily soluble in water. The processing of the hides and skins with the above mentioned salts after having been treated with the acidified aqueous chlorite solution takes about from 5 to 20 hours, according to the kind of the raw materials. A precise definition of the moment when the treatment with the salt solution should begin cannot be given. This moment Will best be determined by removing a piece of the oxydatively treated hide and testing the solubility of the hairs in the salt solution. The necessary quantities of the above mentioned salts are lying between 0.5 and 4% relative to the weight of the hides. These quantities are dependent from the excessive amount of acid in the unhairing liquor. If the processing with the salt or Weak basic solution is done in a separate bath, it is sufiicient to add the salts in amounts from 0.5 to 3% in relation to the weight of the hides, to dissolve the hairs.

The following examples will serve to illustrate the invention with reference to several embodiments thereof.

Example 1 1000 kg. of cow hides were treated in a slowly moving drum with an aqueous solution which in 500 liters of H 0 contained 80 liters of an aqueous sodium chlorite solution containing 300 g. of NaClO /l. and l020 kg. of sodium perborate, the pH of which had been adjusted to 3.5 by the addition of formic acid. The unhairing of the hides was complete after about 15-20 hours treatment. The thus unhaired hides could then be tanned after a short pickle.

The results were similar when dilute sulfuric or phosphoric acid were employed for acidification of the chlorite solution.

Example 2 1000 kg. of calf skins were treated in a slowly moving drum with an aqueous solution which in 600-700 liters of water contained 100-110 liters of aqueous sodium chlorite (300 g./l.) and 25-30 kg. of sodium perborate, the pH of which had been adjusted to 3.3-3.6 with formic 3 acid. The unhairing of .the calf skins was complete after about 20-25 hours. After such unhairing and a short while the hides were ready for tanning.

Example 3 100 kg. of cow hides which were previously soaked and fleshed are treated in a moving drum with a liquor comprising 50 liters of water, 12 to 13 liters of an aqueous solution of sodium chlorite containing 300 grams per liter of a 100% grade of sodium chlorite and 1 liter of 10 aqueous chlorite solution containing an effective amount 20 of an inorganic per compound selected from the group consisting of hydrogen peroxide and adducts of hydrogen peroxide to prevent substantial liberation of C10 and C1 during the unhairing treatment.

2. The method of claim 1 in which said per compound is sodium perborate and the quantity thereof is at least 25% by weight based on the chlorite content of the solution.

3. The method of claim 1 in which said per compound 4 is hydrogen peroxide and the quantity thereof is from about 0.3 to 5%, related to the weight of the hides, calculated on 100% hydrogen peroxide.

4. The method of claim 2 in which the chlorite solution is acidified to a pH of about 3.03.8.

5. The method of claim 4 in which the chlorite is sodium chlorite and the quantity of sodium perborate is 5-8 parts by weight per 7-8 parts by weight of sodium chlorite.

6. The method of claim 3 in which the chlorite solution is acidified by adding formic or sulfuric acid, resulting in a pH value from 3.2 to 3.5.

OTHER REFERENCES Boura: Revue Technique des Ind. du Cuir, Pub. Nov. 1965, pages 334-340.

25 DONALD LEVY, Primary Examiner.

US. Cl. X.R. 96-2 

